[R] Problem with ddply in the plyr-package: surprising output of a date-column

[Peter Ehlers]

On 2011-04-25 13:07, Hadley Wickham wrote:
>> If you need plyr for other tasks you ought to use a different
>> class for your date data (or wait until plyr can deal with
>> POSIXlt objects).
>
> How do you get POSIXlt objects into a data frame?
>
>> df<- data.frame(x = as.POSIXlt(as.Date(c("2008-01-01"))))
>> str(df)
> 'data.frame':	1 obs. of  1 variable:
>   $ x: POSIXct, format: "2008-01-01"
>
>> df<- data.frame(x = I(as.POSIXlt(as.Date(c("2008-01-01")))))
>> str(df)
> 'data.frame':	1 obs. of  1 variable:
>   $ x: AsIs, format: "0"
>
> Hadley
>

To mimic the OP's code

   df <- data.frame(x = "2008-01-01")
   df$x <- as.POSIXlt(df$x, "%Y-%m-%d")
   str(df)
   #'data.frame':   1 obs. of  1 variable:
   # $ x: POSIXlt, format: "2008-01-01"

Peter Ehlers